Molding & Casting

GREEN SAND MOLDING

LLC DPL (Dnepropromlit) is a market leader for the manufacturing of ductile iron (nodular cast iron) produced using the technology of green sand molding with the help of high-performance horizontal flaskless molding machines Heinrich Wagner Sinto FBO-II and Heinrich Wagner Sinto FDNX.

High productivity of green sand molding lines by Heinrich Wagner Sinto, installed in our manufacturing facility, is achieved by highly efficient methods of molding sand mix compaction and absence of necessity for supplementary treatment of the molds. The process of green sand molding is fast, simple, technologically advanced and highly productive.

The enterprise wields a special section of reconditioned sand re-use and a pouring station, necessary to provide full-scale projected capacity of casting with HWS FBO-II and HWS FDNX horizontal molding machines. The whole technological process is machine-controlled, including the preparation of molding sand mixture, molding, additional weights application and removal, as well the casting knockout.

The main advantages of horizontal flaskless molding line:

Functioning with common molding sand mixture with regular bentonite without additional requirement to the mixture and its preparation (as opposed to vertical flaskless molds)

Use of HWS FBO-II and HWS FDNX green sand molding machines by Heinrich-Wagner-Sinto allows achieving the highest results and near-perfect production outcome in respect of quality and range of castings, making the casting and molding process as machine-aided as possible.

The automatic pressure control mechanism of the sand inlet and pressing unit ensures even sand compaction, guaranteeing high quality production of complicated castings even if these involve deep pockets and thin walls.

The compaction process allows the height of the upper and lower mold sections to be varied independently of each other. This significantly reduces sand consumption, improving economy (optimizing the casting / sand ratio).

Below provided is the schematic illustration of molding process, performed with Heinrich Wagner Sinto FBO-II.

Automatic flaskless molding is currently by far the most in-demand mass-production process for molding, owing to such considerably important factors as the absence of flasks, high productivity (over 150 mold per hour), compact size of the machines, grand facilitation of castings knockout process as well as the overall environmental friendliness of the process. Producing castings on Heinrich Wagner Sinto FBO-II and Heinrich Wagner Sinto FDNX horizontal flaskless molding lines ensures highest quality of manufactured castings and homogeneously compacted molding sand mixture.

Below provided is the schematic illustration of molding process, performed with Heinrich Wagner Sinto FDNX:

Main advantages of mold-making with the help of green sand molding process are elaborated and apparent:

Traditional (in good sense) approach and perfectly explored production process

V ACUUM MOLDING (V-PROCESS)

LLC DPL holds a commitment to implement innovations to the foundry process and castings production. Such innovations primarily imply technological advancements associated with the introduction of innovative equipment and production processes.

In 2010, our company completed a purchase of foundry equipment for vacuum molding according to world-renown V-process. In 2012, the vacuum molding production line with rotary table – model VDT-6 by HWS-Sinto (Heinrich-Wagner Sinto), Germany – was launched.

Casting with Vacuum molding process (V-process, developed in Japan) is a characteristic molding process in flasks with the help of dry sand without binding agents, which is being pressed together and held in flasks due to synthetic polymer films and vacuum. During the process of pouring, the film is being permeated by gas, which further penetrates into the mold to be condensed upon the cold grains of molding sand, serving as a binding agent. This method is employed to manufacture a wide range of castings used as housings for gas- and oil-producing industries, components for railway application and other parts, functioning in the conditions of high pressure and aggressive environments.

Vacuum-molded casting is one of the most progressive casting methods, used to obtain high-quality casting with flawless surface quality without additional surface finishing operations (roughness ≈100 microns for steel, for other castings – 70 RZ and higher).

ADVANTAGES OF V-PROCESS CASTING MANUFACTURING:

Mold filling rate during pouring process is higher by 25-30% than during greensand mold filling.

The mold provides for a minimum pouring temperature for metal due to the high filling rate and heat capacity.

The lowest production cost of casting, by 25-30% lower, than the castings made with sand molds and by times lower in cost than traditional cold-hardening mixtures casting – the best solution for mass-production of castings.

No necessity to prepare the sand mixture – the process is carried out with dry sand.

No waste products, sand mix regeneration system and eco-friendliness.

Possibility to produce thin-walled steel castings.

Long service life and high durability of patterns, no contact between the pattern and the sand (only through film, which excludes the possibility of quick wear).

V-process, being a cutting-edge casting and molding technology, has proved its efficiency for manufacturing of iron and special steel castings numerous times. Owing to a highly ecological nature of the V-process in comparison to any other molding processes, the prospects of its expansion and further development are truly limitless.

V-process allows considerably cutting down the cost for investment into the upgrades for casting enterprises and stand-alone foundries. Other than that it ensures the production of more high-quality castings with a far greater economic effect.

A characteristic feature of the process is the inclusion of dry, binder-free silica sand between two plastic films with a sub-pressure of 0.3 – 0.6 bar. This can be compared to coffee or peanuts in a vacuum packaging, for example. What sets vacuum-molded casting – ‘Vacuum casting’ apart from others is, above all, the high quality of the surface and the excellent dimensional accuracy. On certain conditions it can utilized without pattern draft which usually is necessary. That means reduction or even elimination of subsequent machining in individual cases.

The V-process is based on the technology of creating the vacuum effect which draws the thermoplastic film down onto the profile of the correspondingly prepared pattern and retains the mold stability during pouring and cooling including the process of casting knock-out and removal.

Brief description of the V-process as follows:

The pattern is mounted on a closed evacuating case – the vacuum box. Both are equipped with numerous vents. Above the thermoplastic plastic film – the pattern film – which is tensed in a frame, the appropriate radiant heating system is situated. The warmed-up and so to a high degree workable plastic film is lowered onto the pattern.

The vacuum box is admitted with a sub-pressure of 0.5 – 0.6 bar and so the film is sucked accurately to the shape of the pattern. After that a black wash is applied on the film.

Further advantages are:

no pattern wear;

low wall thickness are pourable;

there are no or only small burrs in the mold joint;

the fettling costs are low;

the process is environmentally-friendly and ergonomically favorable.

The double-walled flask, equipped with suction tubes and windows on the inside, is lowered onto the pattern device.

The flask is filled with fine-grained, dry and binder-free sand and is pre-compacted by vibration. The mold part is covered by a plastic film. The sand between both films is pressed together through the atmospheric air pressure by switching on the vacuum.

After switching off the vacuum in the pattern carrier, the mold part which is covered with plastic film on both sides and still is admitted with the vacuum is picked-up from the pattern device.

The drag mold is produced in the same way and rotated by 180° afterwards. Necessary cores are set and the two flasks are put together to a ready-to-pour mold. The vacuum remains switched on during pouring and solidifying of the melt.

During the pouring process the film evaporates and/or burns when filling in the casting metal. Because of the vacuum the residues of the film penetrates into the mold and they form a thin shell with the sand particles which compacts the mold in its skin layer. This process is supported by the applied black wash.

For shaking out the flask the vacuum is switched off, the sand flows out and the casting is free for further handling.

Dimensional precision

Dependent on the special characteristics of the vacuum molding process:

using very fine-grained, graded molding sands,

high and consistent sand compaction,

no wear of the pattern equipment,

less or no need of draft,

possible elimination of vibration table for stripping the pattern off the mold,

no movement of the mold wall due to high mold hardness,

no deformation by volatilizing molding sand additives,

the dimensional accuracy and weight constancy of the castings are excellent. The same applies to large casting dimensions, high casting weights and difficult geometric molds. The reproducibility of the good values at the serial production is excellent; from batch to batch there are no differences ascertainable. Approximately ± 0.3% can be indicated as a reference value for the dimensional accuracy.

The accuracy to size and repeatability of the vacuum casting offer the worker excellent starting conditions; especially the requirements of modern machining techniques with NC- and CNC- machines are met, an adjustment is usually not necessary.

Pouring without drafts

In contrast to castings produced by conventional methods a draft, at least partial, is not necessary. Through reversing the sub pressure during the molding process, that means at lifting the part off the mold from the pattern equipment, there is almost no friction between pattern and film, so that it is also easy to lift the pattern with a draft of 0°. To fully utilize this process-related benefit, an intensive dialogue between the foundry personnel and the design engineers is highly recommended.

The surface quality of vacuum casting is so high that, for example, the often used subsequent shot blasting may even have a negative effect on the surface roughness, since after such treatment the casting would have a far more roughness of surface than exactly after the knock-out of the casting from the mold.

The profitability of vacuum molded castings already starts with the pattern. Because of the plastic film lying lies between the molding sand and the pattern there is no direct contact with the pattern.

The pattern does not wear and expensive metal-or plastic pattern are not required. ‘Simple’ wood pattern with a sufficient stability are enough. Even pattern for conventional machine molding can be used, the necessary air suction bore holes can also be made later without any problems.

High surface quality and low dimensional tolerances reduce the extent of machining and perhaps it is not necessary at all. The latter mainly applies to molding without drafts. The vacuum molding process offers several possibilities to save material and to correspond to the requirements of the lightweight construction. The low dimensional tolerances enable a corresponding reduction of the wall thickness of weight-bearing cross sections. Furthermore, compared to other methods films, the flowability of the casting metal between the coated films is better by 20 %, dependent among other things on the air in the mold and the mold emission which are sucked off by the vacuum during casting.

The high stability of the vacuum molds influences the profitability as well; because it is a prerequisite for the so-called riserless pouring of cast iron materials, with which the output – the relation between liquid insert and raw castings – is improved. In many cases the good characteristics of vacuum casting lead to economically challenging results. Herewith, it is possible to call upon the conspicuous advantages of V-process: